dt-bindings: power: supply: drop quotes when not needed

Id and schema fields do not need quotes.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220726115748.101015-3-krzysztof.kozlowski@linaro.org